1. Field of the Invention
The invention relates to a pressure chamber of a piezoelectric ink jet print head and a fabrication method thereof, and more particularly to a fabrication method of forming a plurality of small-size trenches in a photoresist layer which fills a large-size opening of a silicon wafer.
2. Description of the Related Art
A piezoelectric ink jet print head employs a forced voltage to deform a piezoelectric ceramic body, and uses flexure displacement of the piezoelectric ceramic body to change the volume of a pressure chamber, thus the chamber expels an ink droplet. Since high-temperature gasification is omitted and the piezoelectric ceramic body has a quick response without restriction against thermal conductivity, the piezoelectric ink jet print head has the advantages of superior durability, high-speed print performance, and superior print quality. The piezoelectric ink jet print head has been commercialized into a bend mode and a push mode according to its deformation mechanism. The bend mode uses a face-shooter piezoelectric deformation. When a voltage is exerted, a piezoelectric ceramic body is deformed and impeded by a vibrating plate, thus being laterally and extruding the ink in a pressure chamber. As a voltage difference arises between the internal space and the external circumstance, the ink adjacent to a nozzle orifice is accelerated and expelled as an ink droplet. Comparably, the push mode uses an edge-shooter piezoelectric deformation. When an opposite potential of the applied voltage between the two electrodes is continuously increased, a ceramic sidewall of an ink chamber bends outward to introduce ink. When the applied voltage is rapidly changed, a piezoelectric ceramic plate is deformed to cause a greater bending motion, thus the ink in the pressure chamber is extruded by a right-hand thrust and expelled from a nozzle orifice to form an ink droplet.
Conventionally, the vibrating plate and the pressure chamber are formed by a laminated ceramic co-fired method which includes steps of synthesizing raw powers (such as PZT, ZrO2, Pbo, TiO2 and other additives), mixing, drying, calcining, smashing, granulation, squeezing, shaping, sintering and polarization. The complicated and difficult procedure in the laminated ceramic co-fired method, however, has disadvantages of low yield and high cost and is unfavorable to mass production. Accordingly, a modified etching process for forming the pressure chamber and increasing process reliability thereof is called for.
Currently, in semiconductor etching processing, many approaches to a deep-hole etching technique have been developed and successfully applied to micro electromechanical structures. The deep-hole etching technique, such as a wet etching method through a chemical reaction or a dry etching process through a physical reaction, however, has the drawbacks of directional etching result, low etching rate and excessive process costs. Conventionally, a direct Si-wafer etching process cannot control the profile, depth, and uniformity of the pressure chambers, which causes the piezoelectric ink jet print head to fail in a high resolution performance.